Downtown: Shelia Zaldana, 46

Los Angeles police detectives said the killing may have been the result of a dispute over narcotics and that the victim's 23-year-old son was the original target. (Police gave the victim's first name as Sheila but she was identified as Shelia by the coroner.)

Michelle Cato, 26, was arrested immediately after the shooting on San Julian Street near the LAPD Central Area police station.

LAPD Det. Paul Vernon said Cato and Zaldana lived in South Angeles and while on skid row got into a dispute that investigators believed involved drugs.

"Based on the suspect's criminal background, she was on parole for drug-related convictions, and not living on skid row, we suspect that narcotics was at the root of this dispute," Vernon said.

Moments before the shooting was reported at 3:40 p.m., Cato pointed a gun at Zaldana, "but the gun did not go off," Vernon said.

"As the suspect was walking away, she turned back and fired at the mother and the gun went off, the bullet striking her in the head," Vernon said.

Cato fled south on San Julian Street and then ran west on 6th Street, discarding the small-caliber handgun believed to be the murder weapon on the street, Vernon said.

As she neared the LAPD's Central Division station, with witnesses in pursuit, she ran into a police officer, who immediately detained her.

Vernon said the block where the shooting took place "has more cops and more cameras per square foot than any other block in the city."